One type of dewatering mechanism for separating a liquid such as water, from a slurry such as coal slurry, described in U.S. Pat. No. 4,246,108 by Croopnick et al., uses a rotating circular chamber that rotates about the axis of the circle to aid in the separation. The slurry is fed to a radially outer region of the chamber where water and fines flow radially inwardly past a screen, and where larger particles settle to the periphery of the region from which they can be removed. If the settled particles are allowed to escape too rapidly from the periphery of the separating region, then water and fines may flow with them. Mechanisms such as screw feeders can be used to produce a controlled discharge of particles, but such mechanisms cannot be easily adapted to cover a large curved area extending 360.degree. around the rotating circular chamber. A discharge mechanism which could control the discharge of particles from a fluid-particle separator, which was of relatively simple construction and yet which could cover a large curved area, would be of considerable value in systems for separating the fluid and particles out of a slurry.